1. Field of the Invention
The present invention relates to a double Cardan type constant velocity joint incorporated into, e.g., a steering apparatus of an automobile and utilized for transmitting a rotating force acting on a steering wheel to a gear box.
2. Related Background Art
The steering apparatus of the automobile transmits a motion of the steering wheel to the gear box via a steering shaft, a universal joint and an intermediate shaft, and gives a desired steering angle to front wheels. In the case of a typical steering apparatus, an angle of intersection (joint angle) between the steering shaft and the intermediate shaft is not large, and hence a typical Cardan joint (cruciform universal joint) is employed as an universal joint for connecting these two shafts. As known well, the typical Cardan joint has a nonuniform velocity in terms of transmitting a rotating force in a state where the joint angle is given. The nonuniform velocity to such an extent is not, however, a problem in terms of utility as far as the joint angle is comparatively small. Further, it is also practiced that two pieces of Cardan joints are used to offset the nonuniform velocity. In recent years, however, it happened that the angle of intersection between the steering shaft and the intermediate shaft increases in order to ensure an improvement of security against collisions in some of the automobiles such as cab-over type automobiles, etc. In such a case, if the typical Cardan joint is used, the nonuniform velocity for transmitting the rotating force becomes large enough not to be ignorable. Then, in such a case, it can be considered to employ a double Cardan type constant velocity joint.
Double Cardan type constant velocity joints hitherto known are disclosed in, e.g., Japanese Patent Post-Exam Publication No.50-21610 and Japanese Patent Laid-Open Publication No.7-251746. FIGS. 14 and 15 show the double Cardan type constant velocity joint disclosed in Japanese Patent Post-Exam Publication No.50-21610 thereof. This double Cardan type constant velocity joint 101 includes an intermediate housing 102, first and second yokes 103, 104, a first cross shaft 105 for connecting the first yoke 103 to the intermediate housing 102, and a second cross shaft 106 for connecting the second yoke 104 to the intermediate housing 102.
The intermediate housing 102 among those components has a pair of first support arms 107, 107 provided at one end thereof (a right end in FIGS. 28 and 29) in an axial direction and a pair of second support arms 108, 108 provided at the other end thereof (a left end in FIGS. 28 and 29) in the axial direction in equiphase with each other. Then, first support holes 109, 109 concentric to each other are formed in front end portions of the first support arms 107, 107, while second support holes 110, 110 concentric to each other are formed in front end portions of the second support arms 108, 108.
Further, the first yoke 103 includes a pair of third support arms 111, 111 provided at one end (a left end in FIGS. 28 and 29), in the axial direction, of a connecting cylindrical portion 144 to which an end portion of a rotary shaft (unillustrated) such as the steering shaft or the like can be connected and fixed. Then, third support holes 112, 112 concentric to each other are formed respectively in close-to-front-end portions of the third support arms 111, 111. Moreover, a first engagement protrusion 114 protruding opposite to the connecting cylindrical portion 144, is formed on an intermediate portion of a first connecting portion 113 for connecting mutually the front ends of the third support arms 111, 111.
Furthermore, the second yoke 104 includes a pair of fourth support arms 116, 116 provided at one end (a right end in FIGS. 28 and 29), in the axial direction, of a connecting cylindrical portion 115 to which an end portion of another rotary shaft (unillustrated) such as the intermediate shaft or the like can be freely connected and fixed. Then, fourth concentric support holes 117, 117 are formed respectively in close-to-front-end portions of these fourth support arms 116, 116. Moreover, a second engagement protrusion 119 protruding opposite to the connecting cylindrical portion 115, is formed on an intermediate portion of a second connecting portion 118 for connecting mutually the front ends of the fourth support arms 116, 116.
Then, of first and second shaft portions 120, 121 constituting a first cross shaft 105 in a mutually intersecting state, both end portions of the first shaft portion 120 are rotatably supported inwardly of the first support holes 109, 109 respectively through radial needle bearings 122, 122, and both end portions of the second shaft portion 121 are rotatably supported inwardly of the third support holes 112, 112 through the same radial needle bearings 122, 122. On the other hand, of third and fourth shaft portions 123, 124 constituting a second cross shaft 106 in the mutually intersecting state, both end portions of the third shaft portion 123 are rotatably supported inwardly of the second support holes 110, 110 respectively through the radial needle bearings 122, 122, and both end portions of the fourth shaft portion 124 are rotatably supported inwardly of the fourth support holes 117, 117 respectively through the radial needle bearings 122, 122.
Further, the intermediate housing 102 is constructed by connecting a first intermediate housing element 125 including the first support arms 107, 107 to a second intermediate housing element 126 including the second support arms 108, 108 with a plurality of bolts 127, 127. An angle adjusting member 129 is so provided as to be displaceable in a plane orthogonal to the central axis of the intermediate housing 102, within a slide space 128 formed between the first and second intermediate housing elements 125, 126, which space is defined as an axis-directional intermediate portion of the above intermediate housing 102.
First and second engagement holes 130, 131 are formed in equiphase (concentrically) in both end portions, in the axial direction, of the angle adjusting member 129. Then, the first engagement protrusion 114 engages with the first engagement hole 130 in a freely oscillatable displaceable manner, while the second engagement protrusion 119 likewise engages with the second engagement hole 131. Based on the engagements of the first and second engagement protrusions 114, 119 with the first and second engagement holes 130, 131, angles of inclination of the first and second yokes 103, 104 to the intermediate housing 102 are made coincident with each other.
In the case of the thus constructed double Cardan type constant velocity joint 101, when the first yoke 103 is rotated, a force of this rotation is transmitted to the second yoke 104 via the first cross shaft 105, the intermediate housing 102 and the second cross shaft 106. A positional relationship between the first and second yokes 103, 104 and the intermediate housing 102 changes based on the transmission of this rotating force. This change is, however, absorbed by the angle adjusting member 125 oscillating in the plane orthogonal to the central axis of the intermediate housing 102 within the slide space 128 formed inwardly of the intermediate housing 102.
In the case of the prior art structure using a sliding plate as an angle adjusting member, it is required that a diameter of the intermediate housing be increased corresponding to a displacement of the sliding plate in the diametrical direction of the intermediate housing. Therefore, a diameter of a space (swing circle) for the double Cardan type constant velocity joint swinging when transmitting the rotating force, increases enough to require a larger installing space.
Further, an area of friction between the sliding plate and the intermediate housing is large, and a force needed for displacing the sliding plate augments. Hence, a loss of force when transmitting the rotating force becomes large.
Moreover, foreign matters such as dusts or the like are easy to permeate the frictional surface between the sliding plate and the intermediate housing. If the foreign matters permeate the frictional surface, there must be a progression of abrasion of the frictional surface, resulting in such a problem that the durability declines.
The prior art double Cardan type constant velocity joint 101 described above is constructed such that first and second intermediate housing elements 125, 126 constituting the intermediate housing 102 are manufactured by effecting forge-working or cutting on the metal material. Therefore, this might lead to an increase in costs for the materials and working of the intermediate housing 102 constructed of these first and second intermediate housing elements 125, 126. Consequently, there must be an increased price of the double Cardan type constant velocity joint 101 incorporating the intermediate housing 102.